text:
How to calculate Equivalent Airspeed immediately from Calibrated Airspeed?
I want to calculate each step like IAS -> CAS -> EAS -> TAS
as a chain. Each chain step should depend on the previous step.
IAS is clear. This is a function of pressures. With the Bernoulli equation, IAS = f(p_total - p_static)
CAS is not clear. But I know that static error is taken into account, CAS = f(IAS,static error)
EAS is not clear. I know that EAS takes compressiblity effects into account.
TAS is again clear, dependent on density it is easy to calculate with TAS = f(EAS, rho, rho_0)
How to calculate EAS from CAS immediately
with EAS = f(CAS)?
I know that one can calculate EAS with
EAS = f(Mach, a_0), also by taking in account of
the compressibility of air.
Thank you very much!

I wanted to add to the very detailed and helpful answer above to clarify some things as hopefully it might help someone. Most pilot ground studies courses approach this from the viewpoint of how to go from IAS to CAS to EAS to TAS but skip a lot of detail, which I think is what is frustrating the OP. So here's a deep dive. Also, the previous answer ends with "Solving it for EAS = f(CAS) is left to the reader". Since that's sort of what the OP was asking I thought it might be worth a crack at it, although from a different angle.
IAS (Indicated Air Speed)
This is the speed that the air speed indicator in the cockpit displays. The best way to think of the ASI it that it's a pressure gauge that measures differential pressure (pitot minus static) only it's calibrated in knots (or whatever.) As you say in your question, IAS is a function of (p_total - p_static). Is to what that function is, we'll come to that in a moment.
CAS (Calibrated Air Speed)
What the instrument should have read if the instrument and the pitot/static system were perfect. In other words, the IAS after correcting for position errors (e.g. effect of flap setting on pitot/static system) and instrument errors. CAS can be derived from IAS by using look-up tables but these are aicraft-specific. In modern systems, this is done automatically by the Air Data Computer, so the ASI will directly read CAS. In other words, CAS = f(IAS, hardware errors, Mach, AoA, flap setting, ...) To find out this function, you have to do computational fluid dynamics, wind tunnel testing, flight testing or all three. So it's non-trivial. I can't just give you an equation for it. The good news is, in straight and level flight, the errors aren't usually very big.
EAS (Equivalent Air Speed)
This is where things get weird and annoying. Many aviation courses and textbooks treat EAS as a "stepping stone" to TAS but it's almost never used that way in reality and these sources never tell you how to calculate EAS from CAS. It's usually easier to go straight to TAS from CAS, e.g. using a CRP-5 flight computer (a kind of circular slide rule) or by let the aircraft work it out for you via the Air Data Computer. As a pilot, you very rarely need to actually calculate EAS. CAS, TAS and Mach number are usually far more useful.
EAS is supposed to be a version of CAS corrected for "compressibility errors". This might lead you to think EAS is necessary because the ASI uses some simple non-compressible flow assumptions, which need to be corrected at higher Mach numbers. However, at sea level, EAS is the same as CAS, regardless of airspeed, by definition Wikipedia's definition. I.e. you can be in a very compressible flow regime, like Mach 0.8, and EAS is still the same as CAS. This initially makes no sense until you realise that the definition of EAS has to make an assumption about how an air speed indicator actually works.
One might think the airspeed indicator is calibrated by simply reversing the well-known formula (from Bernoulli) for static pressure, namely:
$q = \frac{1}{2}\rho v^2 $,
like this:
$v_{IAS} = \sqrt{\frac{2q}{\rho}} $,
where $\rho$ is the air density and $q$ is the dynamic (pitot minus static) pressure.
This is not so. Here's where we get to "things they don't tell you in ATPL ground exam courses." It seems that the standard definitions of EAS makes the assumption that the airspeed indicator actually works by using isentropic flow relations. This would require it to know things like the static pressure (it only senses differential) and the local speed of sound (which requires knowledge of outside air temperature.) However, it is still possible to use this approach if you "cheat" and put in sea level values for all the things the instrument doesn't know. In other words, the ASI calculates IAS according to:
$v_{IAS} = a_0 * \sqrt{5\left[\left(\frac{q}{p_0}+1\right)^{\frac{2}{7}} - 1\right]} $
Where $a_0$ is the ISA (international standard atmosphere) sea level speed of sound (340 m/s), $q$ the dynamic pressure as before (aka impact pressure) and $p_0$ is the ISA sea level pressure (101325 Pa).
Note that the magic numbers 5 and 2/7 arise because of the value of $\gamma$ (gamma), the ratio of specific heats for air, which equals 1.4. The more general form is:
$v_{IAS} = a_0 * \sqrt{\frac{2}{\gamma-1}\left[\left(\frac{q}{p_0}+1\right)^{\frac{\gamma-1}{\gamma}} - 1\right]} $
This relation is a well known thing but I don't know how to derive it. Yet. (In any case, this answer is already long enough.)
It turns out that if you take a binomial approximation of the 2/7 power and neglect second order terms and higher, you get this:
$q \approx \frac{1}{2} 1.227 v^2$
The value 1.227 being very close to the ISA sea level density of 1.225, so it is equivalent to Bernoulli for low Mach numbers. Anyway, I digress.
Calculating EAS
From here on, we'll asssume IAS=CAS. Now let us assume you want to find the EAS given only the IAS/CAS and the altitude. Normally, as a pilot, perhaps tackling an ATPL exam question, you'd use a CRP-5, but let's assume we are proper nerds and we want to code this (e.g. in python) or get a better undersanding of how an ADC (Air Data Computer) or ADIRU (Air Data Inertial Reference Unit) works.
The EAS is a function of the CAS, the dynamic pressure and the static pressure.
Finding static pressure from altitude
The static pressure can be inferred from the altitude using the International Standard Atmosphere. For the troposphere (i.e. up to 11km or 36,080ft) the pressure is calculated by solving the hydrostatic equation for a constant lapse rate. Dealing with the tropopause and above is left as an exercise for the reader :-P
$p_s = p_0 \left( \frac{T_s}{T_0}\right)^{\frac{g}{L R}} $,
where $p_s$ is the static pressure at altitude, $p_0$ is the ISA sea level pressure (101325 Pa), $T_0$ is the ISA sea level temperature (288.15K, $g$ is the acceleration due to gravity (9.81m/s2), $L$ is the lapse rate (0.0065K/m), $R$ is the specific gas constant for air (287 J/K/Kg) and $T_s$ is the static temperature at altitude:
$T_s = T_0 - L h$,
were $h$ is the altitude in metres.
Finding the dynamic pressure from CAS
Note that the ASI does not tell you (the pilot) the dynamic pressure directly, it only tells you it in terms of the IAS/CAS. So we have to "reverse" the formula above:
$q = \left[\frac{\left(\frac{v_{CAS}}{a_0}\right)^2}{5} + 1\right]^\frac{7}{2} - 1$
Finding the Mach number
Next we need to find the Mach number. Note that this is a very similar equation to how the ASI calculates airspeed, but this time we use the real static pressure, not the sea-level value:
$M = \sqrt{5\left[\left(\frac{q}{p_s}+1\right)^{\frac{2}{7}} - 1\right]} $
The EAS is then defined as:
$v_{EAS} = a_0 M \sqrt{\frac{p_s}{p_0}} $
In other words, EAS uses the real Mach number but the sea level speed of sound to obtain a speed, and then multiplies this by the root of the pressure ratio. Putting this all together:
$v_{EAS} = a_0 \sqrt{5\left[\left(\frac{q}{p_s}+1\right)^{\frac{2}{7}} - 1\right]} \sqrt{\frac{p_s}{p_0}} $
Epic.
TAS
TAS can be obtained from EAS, which in effect gives another formal definition of EAS:
$v_{TAS} = v_{EAS} \sqrt{\frac{\rho_0}{\rho}} $,
where $\rho$ (rho) is the actual air density at altitude (which can be calculated from temperature and pressure using the ideal gas law ($\rho = \frac{p_s}{R T_s}$) and $\rho_0$ is the ISA sea level density (1.225 kg/m3.) In other words, TAS is just the EAS divided by the root of the density ratio.
However, it's actually easier just to calculate TAS directly, which saves knowing about densities:
$v_{TAS} = a M $
where $M$ is the Mach number as calcuated above and $a$ is the local speed of sound (not the sea level value like the in the EAS formula,) which can be calculated from $a = \sqrt{\gamma R T_s}$.
#!/usr/bin/env python3
#
# Calculate EAS and TAS, given CAS and a pressure altitude
# Warning: only works in troposphere, i.e. below 11km
#
# By Halzephron 2020
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

from math import pi, sqrt
import sys

ms_per_kt = 0.51444
feet_per_metre = 3.28
T_0C = 273.15 # 0 degrees C in Kelvin

# Some useful constants

g=9.81          # Acceleration due to gravity
R=287           # Specific gas constant for air
L=0.0065        # Lapse rate in K/m
T0 = 288.15     # ISA sea level temp in K
p0 = 101325     # ISA sea level pressure in Pa
k = 1.4         # k is a shorthand for Gamma, the ratio of specific heats for air
lss0 = sqrt(k*R*T0) # ISA sea level speed sound
rho0 = 1.225    # ISA sea level density in Kg/m3

# Return knots given m/s
def kt(m):
    return m/ms_per_kt

# Return pressure ratio given a Mach number and static pressure,
# assuming compressible flow
def compressible_pitot(M):
    return (M*M*(k-1)/2 + 1) ** (k/(k-1)) - 1

# Return Mach number, given a pressure ratio d=p_d/p_s
def pitot_to_Mach(d):
    return sqrt(((d+1)**((k-1)/k) - 1)*2/(k-1))

# Given an altitude h, return the temperature, assuming we're
# using the International Standard Atmosphere and are flying
# in the troposphere.
def temperature(h):
    return T0 - h*L

# Given an altitude h, return the local spead of sound, assuming
# we're using the International Standard Atmosphere and are flying
# in the troposphere.
def lss(h):
    return sqrt(k*R*temperature(h))

# Given an altitude h, return the pressure, assuming we're
# using the International Standard Atmosphere and are flying
# in the troposphere.
def pressure(h):
    return p0 * (temperature(h) / T0) ** (g / L / R)

# Given an altitude h, return the density, assuming we're
# using the International Standard Atmosphere and are flying
# in the troposphere.
def density(h):
    return pressure(h) / (R * temperature(h))

if len(sys.argv) < 2:
    print("usage: {} CAS ALT".format(sys.argv[0]))
    exit(0)

cas = float(sys.argv[1])*ms_per_kt # Convert kts to m/s
alt = float(sys.argv[2])/feet_per_metre  # Convert ft to m

ps = pressure(alt)
lss = lss(alt)
oat = temperature(alt)
rho = density(alt)

# First we need to "reverse" the air speed indicator to find the dynamic
# or "impact" pressure. It is tempting to assume that an airspeed
# indicator relates airspeed to dynamic pressure using Bernoulli's
# 0.5 * rho * v**2, but it that is not the case here. Instead,
# a sort of modified compressible flow equation is used. A "pseudo"
# mach number is found as a function of a pressure ratio, assuming the
# static pressure is equal to ISA conditions. The airspeed is then found
# by assuming the local speed of sound is that of ISA sea level.
pd = compressible_pitot(cas/lss0) * p0

# Find Mach number
M = pitot_to_Mach(pd / ps)

# Calculate EAS (equivalent air speed)

eas = lss0 * M * sqrt(ps/p0)

# Calculate TAS (true air speed)

tas = lss * M

# Or we could have used tas = eas / sqrt(rho/rho0)

print(f"Pressure Altitude:     {alt*feet_per_metre:5.0f}   ft")
print(f"Static Temperature:      {oat-T_0C:5.1f} C")
print(f"Density Ratio:            {rho/rho0:6.3f}")
print(f"Pressure Ratio:           {ps/p0:6.3f}")
print(f"Static Pressure:        {ps/1e2:6.1f} mb")
print(f"Dynamic Pressure:       {pd/1e2:6.1f} mb")
print(f"Total Pressure:         {(pd+ps)/1e2:6.1f} mb")
print(f"CAS:                    {kt(cas):6.1f} kt")
print(f"EAS:                    {kt(eas):6.1f} kt")
print(f"TAS:                    {kt(tas):6.1f} kt")
print(f"LSS:                    {kt(lss):6.1f} kt")
print(f"Mach:                      {M:4.2f}")

It is almost a year passed by and finally someone researched this question in my desired degree of details :) Thank you! The explanation gave me a good understanding what questions a designer of adiru is confronted. Most epic is your python solution because this is exactly what I had to do on some crappy way X)

Thank you for your lovely comment, and for approving my answer. I had no idea if you'd find my answer, it being so long ago, but I was going through a similar frustrating situation with understanding EAS myself and wanted to share what I found. I'm so glad it helped.

Hello Halzephron, welcome to aviation.stackexchange. Very nice answer, I hope you'll write more of those in the future! Cheers, DL

Airspeed is measured with a pitot tube. A pitot tube has two pressure measurement ports. One that measures the total pressure $p_t$. This port is facing the incoming airflow. The other measures the static pressure $p$ and is placed perpendicular to the airflow. The difference between the two pressures is called impact pressure (pressure rise do to the airflow impacting the pitot tube) and is denoted $q_c$.
The impact pressure is related to the speed of the airflow the pitot tube is exposed to. If the flow is considered incompressible (which is an acceptable approximation for speeds up to 200 knots) the impact pressure can be derived from Bernouilli's equation.
$q_c = \frac{1}{2}\rho V^2$

$q_c$ is the impact pressure in Pa
$\rho$ is the density in kg/m3
$V$ is the true airspeed in m/s

Equivalent airspeed
The airspeed indicator is calibrated for standard sea level conditions, where $\rho$ is 1.225 kg/m3. In reality the aircraft will fly at altitude and therefor the actual density of the air is lower. Therefor the airspeed as measured by impact pressure will be lower as well. For example if an aircraft flies 75 m/s (about 146 knots) at 6000 ft the density will be 1.02393 kg/m3.
$q_c = \frac{1}{2} 1.02393 \cdot 75 ^2 = 2879.8 \textrm{ Pa}$
The equivalent airspeed at sea level for the same $q_c$ is:
$V_{EAS} = \sqrt{\frac{2 q_c}{\rho_0}} = \sqrt{\frac{2 \cdot 2879.8}{1.225}} = 68.6 \textrm{ m/s}$
Your airspeed indicator (assuming no errors) will read only 68.6 m/s (133 knots) despite the fact that you are moving with 75 m/s (146 knots) with respect to the air.
Conversion of true airspeed to the equivalent airspeed can be done directly by:
$V_{EAS} =V\cdot \sqrt{\frac{\rho}{\rho_0}}$

$V_{EAS}$ equivalent airspeed (m/s)
$V$ true airspeed (m/s)
$\rho$ actual air density (kg/m3).
$\rho_0$ density at standard sea level conditions (1.225 kg/m3)

Calibrated airspeed
The effects of the lower density on your aispeed indicator become more pronounced the higher you go. Once you go faster than about 100 m/s true airspeed the effects of compressibility can no longer be ignored and the above no longer applies. Airspeed indicators are corrected for effects of compressibility and therefore don't use the equivalent airspeed but instead use calibrated airspeed for calibration.
$V_{CAS}=a_{0}\sqrt{5\left[\left(\frac{q_c}{p_{0}}+1\right)^\frac{2}{7}-1\right]}$

$V_{CAS}$ is calibrated airspeed
$a_{0}$ is the speed of sound under standard sea level conditions (340.3 m/s)
$p_0$ is the static air pressure under standard sea level conditions (101325 Pa)
${q_c}$ is the impact pressure

The impact pressure is also a bit more complex for compressible flow:
$\;q_c = p\left[\left(1+0.2 M^2 \right)^\tfrac{7}{2}-1\right]$

$p$ the static pressure
$M$ the Mach number

Indicated airspeed
The airspeed that is actually indicate on the airspeed indicator deviates from the calibrated airspeed because of several error factors:

instrument error
position error
installation error

Instrument error are errors within the airspeed indicator when converting the static pressure and the total pressure to a speed indication. In mechanical instruments these are often more pronounced that in digital systems.
Position error are errors in the position of the static port (not measuring exactly static pressure, but also some effects of moving air) and position of the total pressure port (not exactly measuring the full ram rise).
Finally there are installation errors, which include for example leaking tubes between the instrument and the pitot ports.

Given the above, we can now derive the relation between Calibrated Airspeed and Equivalent airspeed
Calibrated airspeed is dependent on the impact pressure, which is in turn depending on the Mach number.
The Mach number is the ratio between the true air speed and the speed of sound $a = \sqrt{\gamma R T}$.
We can now express the Mach number as a function of the equivalent airspeed:
$M = \frac{V}{\sqrt{\gamma R T}} = \frac{V_{EAS}\sqrt{\frac{\rho_0}{\rho}}}{\sqrt{\gamma R T}}$
From the ideal gas law it follows that $p = \rho R T$ and so we can simplify the Mach number to :
$ M = V_{EAS}\sqrt{\frac{\rho_0}{\gamma p}} $
From this it follows that impact pressure for compressible flow is:
$\;q_c = p\left[\left(1+0.2 M^2  \right)^\tfrac{7}{2}-1\right] = p\left[\left(1+ \frac{\rho_0}{5\gamma p} V_{EAS}^2 \right)^\tfrac{7}{2}-1\right]  $
That brings the relation between CAS and EAS to :
$V_{CAS}=a_{0}\sqrt{5\left[\left(\frac{p}{p_{0}}\left[\left(1+ \frac{\rho_0}{5\gamma p} V_{EAS}^2 \right)^\tfrac{7}{2}-1\right]+1\right)^\frac{2}{7}-1\right]}$
Solving it for EAS = f(CAS) is left to the reader.

Parts of this answer are taken from this answer.

All what is explained here is information that you find in most books, "the easy way", but Im looking for more mathematical explanation. Is there some authors who goes deeper?

Hello @ptiza_v_nebe, I don't understand what you are looking for. All the mathematical relations between the speeds are in the answer, except for the relation between IAS and CAS because that relation is specific to each aircraft. Can you explain what you are missing?

My question is still EAS = f(CAS). How to accomplish this? How does ADIRU calculate all the speeds if it has only pressures from pitot tube and Temperature? Other thing, what you have mentioned is only summarize of all knowledge about air characteristics and using pitot tube. What I need for example is, where does the formula for CAS come from? What are the roots with all physical relations? Is there no author who can explain things about air data holistically?

Hello @ptiza_v_nebe The ADIRU follows these equations and may have a lookup table to correct the for pitot port position errors. For the fundamental physics behind the compressible flow, I would start with the Euler equations. You can integrate these to get to Bernoulli's equation (assume $\rho$ is constant) or to the compressible variant (assuming adiabitic compression), taking into account the appropriate thermodynamic equations. It is a bit too much to cover that here in a single answer.

DeltaLima! You are the best! Thank you!

@ptiza_v_nebe You are welcome! If I answered your question you should consider to select it as the accepted answer (by clicking the green tick mark next to the answer).

@DeltaLima Help me out please. This formula is not working. couldn't resolve this, can you please give numeric example. I solved it by hand it is not working. unfortunately I could not put up an image here. What is solved putting as an answer, as I can upload as an image in the answer.

Given the question:

How to calculate EAS from CAS immediately with EAS = f(CAS)?
I know that one can calculate EAS with EAS = f(Mach, a_0), also by taking in account of the compressibility of air.

The simplest way to get EAS is to reverse the following equation 2:
$V_{CAS} = V_{EAS}*f_0/f = a_{standard}\sqrt{5}\sqrt{(\delta[(1+\frac{M^2}{5})^{7/2}-1]+1)^{2/7}+1}  $
which has a series expansion in M of:
$V_{CAS} \approx  V_{EAS}* [1+\frac{1}{8}(1-\delta)*M^2+\frac{3}{640}(1 - 10\delta + 9\delta^2)M^4 ] $
Which is accurate to 1% below M=1.2.  For the rest of the answer I'll be omitting the fourth order term as it's neglible below Mach 0.85.
f = Compressibility factor
f0= Compressibility factor at sea level
δ = Pressure ratio P/P0.
a_standard = 661.47 knots
But what about Mach vs EAS?
Since Mach is a function of airspeed, EAS appears multiple times in the equation, so for any significant difference between initial guess and actual EAS, an EAS that appears to satisfy the above formula will result in a new Mach value which will require another iteration.  That  relationship is:
$ M = V_{TAS}/c = V_{TAS}/\sqrt{\gamma R_* T} = \frac{V_{EAS}}{\sqrt{\gamma R_* T \rho/\rho_0}} $
where:
γ is specific heat ratio 1.4
R is the specific gas constant for air = 1085 kt^2/K
T is the static air temperature in (in K, not Celsius)
ρ/ρ0 is the ratio of air density at the current altitude to sea level
This allows us to more directly relate CAS to EAS as:
$V_{CAS} \approx V_{EAS}* [1+\frac{1}{8}(1-\delta)*M^2 ] = V_{EAS}   [1+\frac{1}{8}(1-\delta)*\frac{V_{EAS}^2}{\gamma R_* T \rho/\rho_0} ] = V_{EAS} [1+ C {V_{EAS}^2}]  $
Where C is used to simplify the constant terms. Using the ISA model, even though it won't exactly match actual flight conditions, you'd get the following example values for C:

Alt (ft)
Pressure P/P0
density rho/rho0
Speed of sound (kts)
Correction term C (units kt-2)

0
1
1
661
0

10,000
0.6877
0.7385
638
1.299E-07

35,000
0.2353
0.3099
576
9.297E-07

40,000
0.1851
0.2462
573
1.260E-06

For example, at 40,000 ft and -56.5° C you have: 300 knots EAS = 300 + 1.26E-07*300^3 =  334 kts CAS
Getting EAS = f(CAS) from CAS=f(EAS)
Now you may be saying at this point that so far this answer hasn't actually provided a formula that outputs a single closed-form solution for EAS as a function of CAS, and not EAS=f(TAS) or EAS=f(Mach), or CAS=f(EAS). Admittedly, at the time of writing no one else on this page has either.
The simplest solution in real software might actually be to use a lookup table on one of the above formulas such as CAS = EAS*(1+c*EAS^2).  Depending on the solution and the required precision that could actually be faster and more accurate than lots of floating point operations.
If you'd prefer a closed-form solution, a single iteration of Newton's method can give a relatively simple and decently accurate solution:
$ V_{EAS} \approx V_{CAS} - \frac{C \cdot V_{CAS}^3}{1 + 3C \cdot V_{CAS}^2} $
Where C is the factor above which equals $ \frac{(1-\delta)}{8\gamma R_* T \rho/\rho_0}  $
You can also invert the earlier formula for EAS vs M:
$ \frac{V_{EAS}}{a_{standard}} = M = \sqrt{5} \sqrt{(\frac{1}{\delta}[((\frac{V_{CAS}}{a_{standard}})^2/5 +1)^{7/2}-1]+1)^{2/7} -1 } $

For a more condensed explanation of EAS / ATPL studies:
It is the speed at which an aircraft would have to fly at MSL to experience the same dynamic pressure as experienced by the aircraft flying at a given CAS(for a specific pressure ALT).This is also the reason why the the EAS is always lower than CAS.
At Sea Level the CAS is equal to EAS, upto 10000' and below 250KCAS it closely approximates the same.
The measurement of EAS is essential for Structural engineers who are verifying the integrity of aircraft structures as modeled in an incompressible flow simulation.


text:
Flare: low, slow, and uncoordinated?
I'd like to rephrase the question:
Often I forward-slip on final right right rudder.  During this time, I use the ailerons to keep the aircraft headed down the center-line; the aircraft's bank varies slightly from left wing down, to right wing down.
At some point during this procedure, I have right rudder in and a slight right bank.  I believe this is a skid; Is this something I should worry about?  I would very much like to avoid skidding at all times, especially on final!
Previous question, for reference:
Assuming there is a crosswind and the pilot executes a crabbed approach, during the flare the pilot is going to have to use the rudders to avoid a side-load.   My understanding is that this will result in an uncoordinated flying condition and is prone to stall-spin.
However, this (the flare) does not seem to be much of an issue among pilots.  What am I missing?  How is this any different than a skid?

Spinning needs high angle of attack, which in turn needs a high sink rate. If the runway alignment is done a few feet above the ground, there is simply not enough altitude left to build up a high sink rate. The danger is to do it too early, so the aircraft is airborne for more than a few seconds after the rudder command and builds up side speed.

@Peter: Just prior to touchdown, there is often a high angle of attack.

Not that high. Not even close.

Crosswind landings are always uncoordinated. I'm not familiar with big jets, but I believe they simply kick the rudder to align the nose with the runway and let the momentum carry it in the right direction until it touches down, but I might be mistaken here.
In a smaller aircraft (like a piston single) you're taught to drop a wing into the wind and effectively land in a side slip.
This is all perfectly safe, the dangerous situation you're talking about is a skidding turn, where you apply too much bottom rudder, letting the 'inner' wing slow down to the point of stalling. This only applies to an actual turn however, if you're flying straight, coordinated or not, there's still more or less the same airflow over the wings. You could however experience other aerodynamic effects where fuselage and airfoils effectively perturb the air for other airfoils and might cause a wing drop or pitch change, but it depends on the properties of the aircraft.

Basically it's not an issue because we don't get down to a speed where we need to worry too much about a spin.  It takes more than uncoordinated flight to induce a spin.  You have to have a stall first.  You don't stall as long as there's adequate airflow over the wings.  As long as you don't get below ${V_S}_0$ (with flaps extended) on both wings, even if you're cross controlled, you're okay.

I'd argue that you are at a speed where you may stall.  Right before touchdown, you are almost stalling.

Well, the point is, you stay above stall speed.  The idea is to get the plane just above the surface without stalling, and then match the reducing airspeed to back pressure on the yoke so that the stall occurs right as the wheels touch down.  So you never want to be so close to stalling speed that you have to worry about being cross controlled.  If you're that slow, you need to go around.

Slipping during a descent is not particularly likely to cause a stall because both wings are are sufficiently unloaded that they're not likely to exceed their critical angle of attack. Forward slips to a landing are, in fact, a very useful skill to have, especially for pilots flying very light singles (possibly without constant speed props or even flaps) and one that can allow pilots much more flexibility during landings and engine-out emergencies.
You do need to be careful not to flare too soon, as that might cause your airspeed to bleed off to the point were you will either begin to sink too rapidly and touch down hard or, in a really bad outcome, actually induce a stall and run the risk of losing control of the aircraft. It's probably worth noting that this is a concern for normal landings as well.
In addition to that, even if you were to stall the aircraft while in a slip, the aircraft will snap towards the outer, raised wing, reducing the angle of bank (most modern light trainers will generally just return to a more or less wings-level attitude) and making for a much easier (and less harrowing) recovery. A stall during a skid, by comparison, will snap the aircraft towards the inside, lowered wing, and put it into the incipient phases of a spin (and will usually do so in a far more violent and surprising manner than you might be expecting, even if you've spun that aircraft before). This is a much more unpleasant experience (even in normally benign aircraft) and requires prompt and correct action in order to successfully recover.

In the original question, I'd argue that it's a skid, not a slip.  Or at least, too close to call.

It is very much a slip. The realignment with the runway is actually by banking the aircraft; once the aircraft has been lined up, is opposite rudder being applied in order to keep the aircraft in a wing-low condition, without allowing it to turn further. Large airliners do usually make this correction with the rudder, but they don't usually land in a slipped attitude, so all they're aiming to do is correct the aircraft's alignment before touchdown; even that is too brief to be properly called a skid.

habu@ Thanks.  What if, in the process of aligning the airplane with the centerline, the airplane rolls the other way past level.  All of a sudden, you'd be in a skid, right?

@DavidHinkes - in a properly performed slip, the alignment is performed through the use of ailerons and banking; (opposite) rudder is used simply to keep the turn from continuing and to keep the aircraft traveling in a straight line and aligned with the runway. I recommend the FAA Airplane Flying Handbook, page 8-10 for more details https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-4of7.pdf

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
What do I do if I wish to move my software from DAL Level A to DAL Level C?
If I wish to downgrade my software's design assurance level (DAL) from Level A to Level C, what do I need to do? What are the benefits and drawbacks of doing this?

I'm not exactly sure what you are asking. Do you have software that is certified at level A, and you would like that same software to be certified at level C? Or do you have a level A system but you want to have level C software? Or something else entirely?

While I was giving an interview, he asked me about this. What are the consideration you would do if Level is degraded. And I answered as Certification/Verification effort(cost) would reduce, and was not sure that's what he was expecting

If I wish to downgrade my software's design assurance level (DAL) from Level A to Level C, what do I need to do?

DAL level A software is software which, if it fails, may have "catastrophic" results, defined as "Failure may cause multiple fatalities, usually with loss of airplane."
DAL level C, "Failure significantly reduces the safety margin or significantly increases crew workload. May result in passenger discomfort (or even minor injuries)."
So, to move your software from DAL level A to DAL level C, you'll have to reduce the responsibility of your software.  Your software's operation or failure to operate cannot:

result in passenger major injury or fatality
produce a large negative impact on safety or performance of the aircraft
reduce the ability of the crew to operate the aircraft due to physical distress or higher workload (though significant increases in workload is acceptable at Level C)

At most, your software's operation or failure to operate may:

Significantly reduce safety margins
Significantly increase crew workload
Result in passenger discomfort or minor injury

If you can change your software, or change your customer's use of the software (ie, cannot be used or installed as part of a safety critical control system), then the certifying authorities may allow your software to be certified at Level C.

What are the benefits and drawbacks of doing this?

There are only 62 objectives that have to be met, and of those only 8 have to be verified by someone independent of the person who implemented the code that falls under that objective. While the number of objectives is only reduced a little (71 vs 62), the number requiring independent verification is cut by over 75% from 33 to 8. This significantly reduces the amount of work required to meet certification requirements, mostly in traceability.
The major drawback is that your software cannot be used or incorporated into systems which require a higher level of compliance.
So if your software is designed to control actuators and is currently certified to Level A, you might find that it's being used to control flight surfaces on some planes.
The move to Level C may, in that case, not require any software changes at all.  If you stop performing the full traceability, tests, and meeting objectives with independence at Level A, and only perform those necessary for Level C, then your release under this new system will necessarily only be certified under Level C.  The software can no longer be used to control flight surfaces, but if a new plane comes out with electronically adjustable air nozzles in the passenger compartment, it may be eligible for inclusion there where failure would, at worst, cause passenger discomfort and increase crew workload managing complaints about air vents being misdirected or opened/closed when the opposite is desired.
If your software is an autopilot, though, then it will never be used if it doesn't meet Level A.  In this case, there's no way to change your software or process to a lower level and expect it to be used - the usage of the software defines the level to which it must comply.
In most cases, the usage will drive which level the software must be certified to, and there's no real way (or reason) for you to change your level.  It would cease to be useful software at the wrong level.

If you are following DO-178B or DO-178C, you can't assign your software a design assurance level (DAL). That is the responsibility of the certification authority, such as the FAA in the US, Transport Canada in Canada, or EASA in Europe. There are analysis methods that are used to determine the appropriate level.
If a certification authority does downgrade your design assurance level, you will need to meet fewer objectives and fewer objectives satisfied with independence. An objective satisfied with independence means that the development processes and the verification and validation processes are carried out independently. Lower design assurance levels always have fewer objectives and fewer objectives with independence than the higher levels.
If you have software that is designed and certified at DAL Level A, then it can be used in place of software certified at any lower DAL level.

Software is not certified in itself; the certification is always in context of a system on a aircraft undergoing certificatoin. While it is true that software that has the certification artifacts for use in a DAL-A role on aircraft 1 will meet all the requirements for a DAL-C role on aircraft 2, nonetheless the DER (and ultimately the certifying authority) must be presented with the artifacts and acknowledge that it meets DAL-C before aircraft 2 can be certified.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What would be a suitable aircraft for a short haul freight forwarding business?
I just graduated with an Aeronautical Science degree and I am planning on starting a freight forwarding company.  It would need to be high payload capable and relatively fuel efficient, the route that would be flown everyday is only 300 miles one way.

Is the business to make profit, or is it a prestige project?

It is a business to make profit and expand upon.

For that, I'd have to know where the route is, how big of a payload we are talking about, and the conditions of the airfields at either end of the route.

The route being flow would be from Ft Lauderdale to Havana.  Pay load would be around 4000 - 5000 pounds.  Conditions of the destination airfield are good.

Cigars on demand?... As Carlo mentions, the Caravan is a solid bet. They are flown all over the world, potentially easier to get parts for than some of their older counterparts and from my understanding, reliable. They also run Jet-A which is easy to get at most airports. 100LL is not always available outside the US (in large quantities if at all) so avoiding piston options is something to think about.

Metroliner or Beech 1900.  Stay simple.

Check out what the local contract UPS guys use. You know that they are the low bidder for the route. so costs are low, and uptime must be high or else they would lose the contract. Ours uses Fairchild Metroliners.

You would have to provide more answers to the comment I made above.
But for a relatively small payload (<4000lbs), I'd say you can't go wrong with a Cessna C208 Caravan.  You can buy a good used C208B Super CargoMaster for just shy of $1 million.
Another recommendation for that route would be the DeHavilland DHC-6 Twin Otter.  Payload is increased by 1000 lbs or so over the Caravan and you have the additional safety of two engines for over water operations.  The downside is that these aircraft are fairly prized and will set you back about $ 3-4 million.
Another heavy lifter with an excellent reputation behind it, even after 80 years of service, is the venerable Douglas DC-3/C-47.  You call, we haul 6,000lbs to just about anywhere within fuel range.
All of these aircraft are extremely rugged and have a good reputation after decades of hard use in bush flying.  They are capable of operating on short, rough airstrips - a good benefit in case you decide to expand to more remote destinations within Cuba and can carry tremendous loads.  They're also turbine powered using PT6 engines (except for the DC-3) so fuel is readily available anywhere in the world as is maintenance and spare parts.

Thats what I was thinking.  Thanks for the response.

The Beech 99 could also be a good choice, though it might be hard to find any available as I understand most are already in use by freight companies. Payload capacity is around 3500 lbs.

The Cessna 208 was pretty much designed for FedEx and they use them extensively as feeder aircraft. That would indicate it is probably ideal for the role. Another possibility for a twin is the Fokker/Fairchild F-27 which FedEx used for a long time as feeders.

There are turbine refits of DC-3s too. Didn't check price though.

Are you a pilot?  Are you familiar with aircraft regulations and operations?
I would avoid radial engines.  I would seriously consider planes powered by TPE-331over the PT-6.
The Metroliner will haul about 5000lbs over that distance.  They're airliners and have maintenance bills to match.
The MU2 is also a popular freighter.  Somewhat smaller than the Metroliner it is still an efficient plane.  It requires special training.
The Beech 1900 is also a popular freighter but I would prefer a Metroliner due to the longer engine life and better fuel economy.  Like the Metro, they're airliners and will require some good maintenance.
The Beech 99 is a popular freighter.  I've never flown one but it has a reputation for reliability.
For piston aircraft, the Cessna 404 will lift about 2000lbs.  I love the plane but the engines can give you trouble (@ $50,000 each) if flown by a low time or poorly trained pilot.
The Piper Navajo (350hp) is also a common freighter.  It won't lift quite as much as a 404 but it's a solid machine.
The Cessna 401/402 line is also good.  On par with the Navajo.
You'll also need an air carrier certificate.  Have you started that process?

I would NOT recommend an MU2 for a neophyte pilot.

Agree, but with good training it's not bad.  If you look at the accident rates before and after the SFAR you'll notice a huge improvement.  Still, the Metro/Merlin and MU2s are "big boy" planes and must be taken seriously.  You don't just hop in and go.

@CarloFelicione what are the issues with the MU2?

The aircraft has had an unusually large number of accidents in its service history with over 330 fatal crashes in its service life, most involving engine failures during takeoff and landing.  This is a crying shame as the MU2 is a fine aircraft with good flight characteristics if handled properly.  In 2005 the FAA did a safety evaluation of the MU2 and found the aircraft was safe, if handled properly but mandated type specific initial and recurrent training for MU2 operators (Mitsubishi even went so far as to recommend the creation of a type rating for the aircraft).

I agree with Mitsubishi that the MU2 should require a type rating but apparently the FAA is satisfied with the section 108 training.  It demands a pilot who can fly it by the numbers and react quickly and correctly should an engine loss occur at low altitude because it can bite when cornered.....

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
General dimensions for a uav type rc plane?
I want to build an rc plane that looks like this one

What are the general dimensions that I should follow? I dont want to copy other designs of real uav's and scale them down. A drawing would be great
I want to build something small, wing span should be about 125 cm

What exactly are you asking for? If you're building it then I assume you already know how big you want it to be? And designing and building an aircraft - even a small one - is far too broad to answer here. Maybe you can break down what you need into several smaller, specific questions?

I second @Pondlife. For instance, how to scale just the wings or thrust of a plane.

The wing should be no more than 125cm wide

@zero First you need to work out your payload weight, and using interpolated data from similar aircraft what additional weight you need to assume is for engines and the airframe. from that you can scale the lift of the wings.

You can start by looking at plans here to get a general idea. When it comes to planes you can't just get some "general" measurements and wing it (pun intended). There are a lot of considerations when it comes to making things fly. With out going into specifics it would be best to use known working plans to build something as apposed to trying to throw something together that looks right.
To Answer your question directly that picture looks like the wing span is the the 3.5 foot range, the center section is about 2.5 feet long and tail poles are about 18 inches.

That picture makes it hard to get a sense of scale, the wingspan is actually 3 m.

Oh man that is way bigger than it looks.


text:
What is the optimal altitude for performance and mileage in normally aspirated GA planes?
Given atmospheric condition, a typical common engine (say, Lycoming 4-cylinder), and a fixed-pitch normal prop:
What are normally the best altitudes for:

ground-speed and
fuel efficiency (range)?

Is it always highest (reasonable) altitude (say >=10,000')?  the air resistance is low but so is the engine power,  or is it usually some intermediate altitude?
Does it depend on the aircraft?  Is a Cirrus SR-20 different from a Vans RV-9 from a Cessna 182 from a Piper Cherokee?
How does the efficiency of a piston aircraft change with altitude? covers a lot of ground about the primary forces (air resistance and (normally aspirated) piston/prop efficiency) and secondary forces. But it does not answer how these forces typically combine to create "best" altitudes (for mpg and gs).  The question ultimately was about how these forces could create typical optimums at different alternatives, and whether they could be different for an SR-20 or a 182.

The answers to https://aviation.stackexchange.com/questions/32830/how-does-the-efficiency-of-a-piston-aircraft-change-with-altitude cover a lot of the ground of this question.

First off this highly varies by aircraft. Piston aircraft that fall under the GA header these days have a pretty wide range of altitude capabilities. The Piper Archer I fly wont really get over 10,000 but you can get your instrument rating and grab a Mooney Acclaim which will take you well into the flight levels and get you up to 25,000 Ft.

best altitudes for ground-speed....

The simplest answer here is the altitude at which your tail wind component is the best. Wind speed and direction does shift with altitude and in many cases your [(increased performance/cruise time) + tail wind - (reduced climb speed/climb time)] is best where ever the tail wind component is greatest and your climb does not take impractically long.
Very Generally speaking performance increases with altitude to an extent. However climb rate usually decreases so there is a break even but it for sure varies by airframe and configuration.

fuel efficiency...

Again this varies by aircraft as well as how you chose to operate the plane. Things like running lean of peak can effect efficiency at the cost of speed typically. Some planes have little to no change in endurance at varying altitudes (although your change in airspeed may allow you to cover more distance). At 75% power my archer has almost no change in endurance as I climb.

Variable pitch propellors also offer a great deal of power setting options that can allow you to tune your efficiency even further.

thank you, dave.  (per my question, the acclaim is not normally aspirated, however, and variable-pitch props are not fixed pitch.)  but very important, wind speeds at altitudes will be of major importance here.  going east, higher is probably better.  I guessed that different airplanes may have different "best" altitudes, but for the same one, I had hoped to learn "higher within its max altitude is always better" or "usually intermediate is best."  your answer suggests usually the former.  thank you for the advice.

@ivoWelch the east west prevailing winds is a factor generally speaking although in my personal experience day to day weather at lower altitudes (GA altitudes) and over shorter GA capable distances varies heavily.


text:
Estimating Helicopter Altitude Above Me Based on Webcam Triangulation?
I believe I have police helicopters that like to buzz around at altitudes of about 500', in a town-like area.  If this happened once a day, it wouldn't be a big deal, but it happens more like once an hour. (yes, I am a pilot myself, so I am generally aviation friendly, and I am not anti-police, either, but this is a bit too much.  they ought to be able to climb to 1000' or higher.  there are people on the ground, too.)
unfortunately, they also don't seem to have their ADSB switched on.  I can't even complain, because I can't accurately report altitude.  what I need is a program that can spot an object, presumably with two webcams, and triangulate a moving object.  I know it's a long shot that such a device or program exists, but if it does, I would love to find out about it.  if you are aware of one, please post.
PS: Some comments asked why I bother.  I called to complain to the police, but they politely deny that their copters are regularly flying this low.  I know it's hard to guess altitude, but I think I know when a helicopter flies within 300' of my house at less than 500'.  Can I stop them?  No.  Do I want to reduce helicopter flights?  No!  We need them.  I am just trying to induce them nicely to become more reasonable.  If not, our concilwoman may be able to complain with some data.

Webcams exist.  Sextants exist.  Otherwise I doubt something as specific as you are asking for is readily available.  Likely your question might be closed as a resource question, or off topic, but I'd consider non-aviation avenues for an answer.  e.g. surveyor equipment, laser levels for construction, etc.  P.S. you can complain, you will just be lacking hard evidence.

Also, from a photo of the helicopter over something like a building of known elevation and dimensions it is possible to do the measure and so math with angles to determine height.

If you want to complain, just call them and complain. What they're doing is legal so what's the point of collecting evidence?

Who are you attempting to complain to that requires exact altitudes? The FAA's low flying aircraft reporting only requires that you give an altitude estimate and explain how you estimated it (and photos are helpful here). But just FYI, if you're attempting to gather evidence that they're flying below 500' in a populated area so you can make a complaint to the FAA, realize that helicopters are exempt from that rule provided they don't endanger anyone on the ground.

Knowing the heli type and thus the rotor diameter, a camera lens of known field of view gives you the distance to the heli.  But height above ground isn't that trivial.

@CamilleGoudeseune: as you said, distance is easy to calculate, but you miss that angle is also very easy, you can do with nearly any phone (inclination), so you can get altitude.

@GiacomoCatenazzi, smart!  Please post our two comments as another answer, for when the local terrain is flat.

@CamilleGoudeseune: it will take too much time (so maybe later). It doesn't depend on flat terrain: it work very well on mountain: all star-tracking application work so, but I used standard apps to prepare myself for a solar eclipse (to check if mountains will hide sun too early). -- probably a different way to "triangulate" as the OP may have think, but by having fixed size object (and large), distance is easier to calculate as std method (as you wrote)

Webcam triangulation is actually much more difficult than you would think. Webcams are not designed to measure angles, so the only way I could think of making that sort of system work would be to position two or three webcams, then have an aircraft fly through the area several times. If you were able to feed very accurate position and time data (synchronized to the webcam recording time) you could use machine learning to train the cameras to determine position and height to a reasonable degree of certainty. That's a lot of work and requires you to have that position data.
Otherwise you would have to make cameras which had angle lines painted on the webcam surface, then develop a system to recognize those lines. That's also a lot of work.
A much easier option would be to get a cheap laser rangefinder and put it on a tripod where you can measure the angle above the horizon. As long as the tripod is on a level base if you know the distance to the target and the angle above the horizon you can use simple right triangle trigonometry, where height above the ground would be the hypotenuse times sin(angle).
So H = Range * sin(angle above the horizon)
However, there are considerations here. There will be a bit of inaccuracy inherent in trying to range find and get the angle of a moving object, if you have a hovering chopper that's easier. Also, the height above the ground where you are may be different from the height above ground where the helicopter is.
There's also the fact that pointing lasers at aircraft, even one that is in the infrared like a rangefinder, could get you in trouble even if it isn't strictly illegal. In any case the police almost certainly have permission to fly below 500ft if they are in fact doing so, in which case it's hard to see what you'd accomplish.

Unless the chopper is quite close it will be difficult to get an accurate measurement. Assume it's at 500 feet AGL 1nm away. The actual angle is 4.7 degrees. If your angle measurement is off by only a degree that gives you about 100 feet of error in the altitude estimate.

Please don't shoot a laser, any laser, at an aircraft, ever.

Laser rangefinders are invisible and aren't going to damage anyone's eyes @RalphJ, however I agree it's not what should be done.

Perhaps one could use automotive radar equipment for this task

@RalphJ Laser rangefinders are invisible and, more importantly, dim enough that they can't damage your eye even from point blank range. Pointing them at aircraft is perfectly safe and as far as I can tell even legal.

Actually,webcams are perfectly capable of measuring angles (that's the only thing they can do;what they can't measure is distances). There's a unique mapping of every direction around the lens axis to a pixel coordinate. With ideal optics it's just simple linear algebra, various aberrations make it more complicated,but still feasible to model accurately. No need for machine learning at all (that would normally be used to identify objects in the picture,but that part OP does not need to automate).

it seems like the obvious goto solution would indeed be a rangefinder, such as those used for golf (905nm Class 1 Laser, Laser output <5mw).  they even give altitude.  alas, I really wish I knew whether this is both legal and reasonable.  Even if it is legal, I wouldn't want to annoy the copters.  However, if it is legal and invisible to them, this would be a great solution.


text:
Why are the strings on paramotors so long?
I don't completely understand why the strings on paraglider/paramotors (connecting the vehicle/person to the parafoil) are so long. Couldn't they be made shorter to reduce the amount of space used? It just seems like an unnecessary feature. Sorry if I'm missing something elementary.

When you are asking "why isn't it done differently", it helps to explain what problem you are trying to solve.    Paragliders have long cords.  So what?

@Simon Thanks for the response! I think the main problem is the amount of space having such a large structure takes up. You could make it more compact and still have the same result if you could shorten the cords. This would help if, say, you had lots of people/vehicles mounted to parafoils. I've been thinking about a related concept for a while and shortening the strings would be useful; the parafoils would simply be used for cruising and gliding once in the air, so they wouldn't have to store fuel and so forth.

@bobthepie, you could reinforce the structure. It's called a hang glider. However, that loses the main advantage of a paraglide—you can no longer pack it into a back-pack small enough for to carry around on your back. And even with the motor it still packs much better than the hang glider.

I don't understand what you mean by "amount of space".  I don't see how it could be smaller than packed away in a back-pack

The answer to this is mechanical leverage.
For this, you must understand that the center of mass for a paramotor is usually just above the pilot's head, and that the center of lift is more upwards.

The shorter the strings on a paramotor, the harder that it is to climb, because the length of the effort arm is reduced, requiring a greater power to tilt the paramotor into a climb.
As the motor power increases, you don't actually go much faster. You tip backward, and maintain speed. This is what helps you climb, essentially comboing the wing with the elevator.
The long strings allow for slower, more efficient flight by increasing leverage. This is the same mechanics that are used in most trainer crafts (outside the military) to allow the learner a long, slow flight.
2023 edit
I was reviewing this answer, and realized that I explained the  pitch leverage, but did not explain roll leverage, and the benefit that long strings have in this scenario.
In the spirit of the old answer, consider this front view of a paraglider which is flying.

Ft in this case is the tension force that the pilot feels from the outermost lines. It is made of two components. The horizontal component, Fh, is how much the lines pull outward on the pilot. The lift force, Fl, is the amount of lift force that a pilot feels in flight.
As you can see, Fh is not an especially useful force. While it keeps the glider's shape rigid, which is good, but you're sacrificing lift to do this. by increasing the line length, you can get rid of unneeded  rigidity, and in its place directly increase the lift. There's a balance to be struck here, as with all things aviation.


text:
What role do the winglets on the next-generation 737 play?
I've flown on a couple of 737's recently and noticed that the wings are quite beautiful and have a distinctive upward sweep at the wingtip, almost like a vertical stabilizer.
What advantages and what disadvantages (if any) does this type of wing provide?  I imagine there is some gain in overall stability.

The winglets are for reducing drag. They reduce something called a wing tip vortex and make it weaker increasing efficiency, range, and lift.

The wing tips calling as "sharklet" at Airbus A/Cs and "winglet" at Boeing A/Cs. It reduces the tip vortex and helps to prevent from airflow seperation at wing tips. It have positive effects on both fuel consumption and turbulance making. Negative effect of the additional part is increase of the drag coefficent but you can keep it negligible againts the positive effects.


text:
What type of aileron is the AIrbus A380 equipped with?
The ailerons of the A380 seem to be in 2 pieces. What is its purpose?

Actually, there are 3 ailerons (not 2). This picture shows them better. You can see the third one in your picture too.

What is the purpose of having 3 ailerons?

I guess the purpose is discussed in the question linked. If you feel that the other post does not answer your question, please edit yours and specify why this one is different than that one. It will be reopened then.

also relevant: http://aviation.stackexchange.com/a/11337/1467

This is a duplicate question but there should not be a need to downvote.


text:
What is the cause of the noise heard when the landing gear is deployed?
Why is it that on most airliners, when the landing gear gets deployed, you always hear a loud noise like a bang. Is this due to the equipment locking in place or is there some other reason? As an external person I would think that there should be a mechanism that pushes it down slowly, avoiding this noise but it doesn't seem the case.

The locks release and typically the gear falls free into place.  It is often aided by hydraulic motors (i.e. to overcome anything that might be trying to hold the gear up, such as slush from the takeoff runway that froze after the gear was in the well), but most landing gear will freefall into place within a couple of seconds even without hydraulic assistance after the uplocks are released.
What you're probably hearing is the sudden onset of the wind noise -- when retracted the landing gear is streamlined, but when extended there is now an open cavity where the gear had been, and this open area in the fuselage creates a lot of wind noise from the suddenly turbulent airflow.  Going from a relatively quite state to a loud one suddenly gives the impression of a "bang."  This is possibly enhanced by whatever noise is made by the uplocks that hold the landing gear in place releasing, and perhaps some louder noise as the initial moments of the gear extension may be noisier than the steady-state noise of being fully extended.
Also, the noise due to the turbulence will subside as the airspeed slows, and extending the landing gear often comes during a phase of flight when the airspeed is being reduced in preparation for the final approach segment and the subsequent landing.

These can be quite significant (scary) events on some aircraft.  A Bombardier CRJ aircraft, especially if you are sitting around rows 8-12 near the hydraulic bay and wheel wells, can be a jolt even if you're prepared for it.
I agree with Ralph J and his answer is quite good.  I would like to add a couple of items:
1) An intital "bang" that you hear before the start of the wind noise is either the door uplock or landing gear uplock that is releasing or the hydraulic selector valve that is now porting hydraulic pressure to the uplocks and actuator.  A typical design would have an electric solenoid valve open which directs hydraulic pressure to one side or another of a valve that slides over and opens a port to send the hydraulic pressure to release the uplocks and actuators to power down the gear.  The solenoids act very quickly (within miliseconds) and when you have a hydraulic system at 3000psi the valve moves very quickly and you get a hydraulic "hammer" from the almost instant change in pressure.
2) The noise when the gear is finished retracting and the wind noise has gone away is typically the uplocks locking and is basically the reverse of #1.
Normally you sequence the release of the door locks and gear uplocks before the actuator starts to pressurize, but if its not quite timed right you can get some force built up on the uplocks and when they unlock there can be some noise.  But normally the "bang" is the hydraulic pressure.
You could make this event less dramatic by adding in restrictors and sequencing in the system, but you are adding cost, complexity and weight, and may reduce reliability by having additional failure modes or possible clogging.  As in all things in aerospace, it is a trade between weight, cost, reliability and performance.

scary?  Is the hyperbole necessary?

Beyond whatever particular sources of noise might be associated with an given airliner's landing gear deployment (unlatching, hydraulic pumps, drag brace latching, wind), it should be noted that the sound of a landing gear free-falling into position is not one of them.
Landing gear don't free fall.  Under normal operation, the rate of downward motion as the strut swings into position is regulated by a hydraulic cylinder (e.g. deployment time would be similar even in zero gravity).  Even for a zero-hydraulic-system-pressure "hydraulics out" condition, deployment rate should appear close to nominal because hydraulic fluid already in the cylinder has to be forced out (by the weight of the landing gear) through a relatively small outlet.
A true free-fall would only result from something like fracture of the hydraulic cylinder's piston rod.  In videos of this FAA-required test, a shock strut (typically with deadweight in place of the tires/wheels/brakes) will be seen rapidly swinging to its full down position with tremendous noise and shock at the conclusion.


text:
Is there a database of airport ceilometer raw data?
I am interested in obtaining raw ceilometer data, to test some cloud/aerosol layer identification algorithms.

Is this type of data freely available or will I need to ask for it directly from the airport?
Do airports keep an archive of raw data or simply of cloud heights as determined by manufacturers algorithm and provided in METAR reports?

I think that would be best done in cooperation with meteorological department of nearby university.

I am working for the meteorological department of a nearby university :) The thing is that I wanted to know if there is some kind of freely available online database. Anyway, I will contact the local airport and meteorological service, and see what they can do to help me.

OGIMET looks like it goes back to 2005.
My favorite weather site Weather Underground has historical data.
It seems like you need to plug in dates one at a time but there are plenty of ways to skim a page and im sure you can ask them for a data dump if you know what you need.

Thank you! I already knew about these websites, and they are very good at what they do, but I couldn't find what I was looking for in their archives. They have METAR reports which will be useful when ceilometer manufacturers' algorithms are compared to mine, but I still need the raw data to put my algorithms to use.

@WizardInBlack it may be worth reaching out to Wunderground and asking if you can pull some of their raw data, ya never know, they might let you.

I accepted your answer as the most useful one. I am still waiting for answers from Wunderground and Ogimet.

Weather Underground is a great site, although finding the specific link for archived METAR reports is more difficult than it should be. The following link is an example that gives all METAR reports for a given airport on a given day; you can either use the fields given on the page to find other dates & other stations, or you could edit the URL itself to find what you want (and perhaps even automate that into a screen-scraping app):
Weather Underground Link
You can also get the same data in a CSV file with a separate link.
If you don't mind doing a little bit of coding, you can also subscribe to their API, which allows you to get historical data with some fairly straightforward calls to their API.  The "developer" subscription is free but limited in how many calls you can make; more expensive subscriptions allow more calls.  The following link is where you can start learning about their API.
((This answer is as much an answer to this question, which is now closed and marked as a duplicate of this one.  It is a slightly different question, and this answer is really more aimed at that question, but it addresses this question as well.))

Weather underground does not provide CSV data for free any more :-(

The NCEP Meteorological Assimilation Data Ingest System (MADIS) data archive has global METARs going back all the way to March 2006. If you're interested in just the US, you can find data for 2001 through 2020.
For example, here are the hourly METAR files for June 6, 2011.

I have been looking for this kind of historical data for a long time, and I finally found it!
Check out Iowa State University of Science and Technology's site, called IEM (Iowa Environmental Mesonet). There is even a python script you can use to download it programmatically if you wish! It has various forms of data (maybe not for all networks) going back to 2000 for ASOS and 1995 for AWOS.
It has worldwide data, you just have to switch to the network you want and choose the reporting station!


text:
How much would it cost to fit and maintain every passenger life jacket with personal beacon?
About a year ago one sailor showed his fancy life jacket. It included EPIRB or also known as personal beacon.
To date, the smallest personal beacon I managed to find is Fastnet 220, which weights 150 grams and has battery life of 6 years.
Given the scale of airline industry, how much would it cost in installation, maintenance and fuel, to fit each passenger life jacket with such device, excluding the device cost itself?
Edit: Total weight per 200 seat airplane is 30kg. Perhaps someone can translate to fuel/$ per year per whole industry?
From Thomas Cook PDF, I found that life jackets are audited every 12 weeks and takes up to 40 man-hours per aircraft although they've implemented RFID tags now.
Regarding points outside the original question scope:
The device cost can also decrease to few dollars if they are manufactured in mass scale.
Certification is also a factor. Feel free to estimate it as well if you are familiar with the industry.

You missed the "certification" cost category, which is substantial in aviation.

Even the ordinary consumer model is at least a couple hundred USD. I can't imagine an airline fitting every life jacket with an expensive device that will get used approximately never.

I'm not sure of the advantage of doing this? Have there been a significant number of people (i.e. > 0) lost at sea after an airliner crash who were believed to have survived but couldn't be found?

I was about to say exactly what FreeMan just said. I can't imagine how this would have helped in any scenario that has ever happened or how it would help in any scenario that is likely to happen. Also, at a weight of 150g and battery life of 6 years, this is almost certainly much lower transmission power than the ELBs already on the aircraft. I'm also not sure that the "how much would it cost" question is really answerable, except maybe to an order of magnitude, though the answer is almost certainly "a lot" (mostly for certification and maintenance.)

This serves two purposes. In an event of total airliner disintegration to water, number of transponders would send out signals with exact accident location. In an event where aircraft lands on water and passengers have to put on life jackets, but eventually spread away from the craft, it would be easier to locate them.

@Dzh That is correct, however you need to keep in mind that emergency landings on water or even accidents that result in the plane disintegrating in open waters are not very common and thus, the cost of doing such upgrades vs the probable benefit is something that airlines will most likely not consider it.

@Dzh: If the plane is making a controlled ditching, the chance it fails to transmit it's coordinates is very small. I haven't heard of case where airliner would loose power completely (RAT and batteries provide backup) and there are several methods for sending distress signal. If the plane is not making a controlled ditching, nobody will survive anyway.

For calculating the cost of 30Kg just calculate the missing potential incomes. 30Kg is a little bit less of half a person. So just calculate that per day.... imagine a 300 euros per trip make it 4 trips a day, that's 1200 euros. Each day each airplane will lose 500 euros. (you can challenge cost per trip and number of trips... but losing will be around 200-1000 euros range)

@TrebiaProject. a more realistic way to estimate would be calculating based on suitcase price, which on a ballpark of €30, which includes the taxation, administration, etc. I am more interested in the raw fuel price. And once again, I am not discussing viability or practicality in this thread.

I'm not so sure mass production could get cost down to a few dollars. Is there a reason you think further mass production than already happens can lower the cost by two orders of magnitude?

@Dzh I think is better to perform the calculations based on opportunity lost by airline, if you want to perform a business case is the best option. However, the average passenguer is 75Kg + baggage... so I should have used 100Kg in my quick computation. Anyhow, does not change the order of magnitude.

That is one way to look at it. That would exactly convert to 0.15% of more weight per passenger. Provided the total passenger airline industry revenue is 600b USD per year, the cost of fuel could be expressed as 900m USD.

The extra weight is roughly the weight saved by the introduction of iPads to replace paper. That's apparently saving close to $10K per plane, so you'd expect a similar cost for just flying all those beacons around.
That said, why do you need a full beacon for every vest? If your vests end up scattered over even 10 kilometers distance, you won't have survivors. What you need is a few beacons to locate the plane, and the medium-range active RFID tag on each vest. Such a tag only responds to queries originating nearby. This cuts down dramatically on the battery requirements, as the RFID tag is generally asleep and only woken up by the interrogation signal. Such RFID tags would cost about $20, and weigh a few grams. Battery life is similar (6 years) as that's just chemistry.

Can you please source your first paragraph, or is this just your opinion?

That is good proposition, but is there end device that works already?

@CGCampbell: Delta claims about $13 million in fuel and has about 800 planes. Net savings are probably lower because the devices aren't free

@Dzh: I've played with those RFID tags a decade ago. We could read them even when we put them in the fridge of the building next door.

@MSalters Is THAT your opinion, or can you SOURCE it? Please provide a link to a document that moves it from your opinion to fact backed by sources. :)

@CGCampbell: It's on the delta site

@MSalters, I see, those must be the active RFID tags. It's definitely viable technology, just that it's not an end device.


text:
When to slow down to Va for turbulence?
I'm trying to figure out when it is safe to continue at normal cruise speed and when I should slow down to avoid over-stressing the airframe due to turbulence. (of course I have asked instructors but I'd like to get some more opinions)
My aircraft has a maneuvering speed listed, Va, also listed as the turbulence penetration speed. When should I actually slow down to this speed (i.e. light, moderate, severe turbulence)? How long should such turbulence occur before I slow down (after a bump or two, when the turbulence is observed to be intermittent or continuous, should I slow down immediately)?
For the scope of this question I'm asking specifically about light single-engine general aviation aircraft that cruise around 140 kts. Va is 112 kias. I'd be interested in hearing about larger/smaller aircraft too though.
Answers from actual pilots with experience in this area, please (I would hope all pilots have some :-) ).

I'm just curious what you're hearing from your instructors that you'd rather trust a bunch of (apparently rather knowledgeable) strangers on the internet instead.

I personally would never knowingly fly into conditions where I thought I'd need to slow to Va in a light aircraft as that means conditions are pretty severe.

@GdD, I disagree.  There's nothing too dangerous about garden variety turbulence.  A hot summer day over the desert will generate some nasty bumps but I'd never cancel a flight for safety reasons.  It's just extremely uncomfortable.  Mountain waves (rotors) and thunderstorms are another story, however, and must be respected.

@acpilot I agree with you. Try to avoid all turbulence and you're not going anywhere. Any pointers for me on when it's time to slow down?

When you encounter moderate turbulence, say within the bounds of an AIRMET T, you should slow to Va corrected for the aircraft weight at that time.  This advice can be Googled with ease, but here is a decent site: http://www.mountainflying.com/pages/mountain-flying/turb_va.html

@acpilot funny, that's the same site I found the other day!

To help you understand this, I feel like we should discuss how Va is determined.
14 CFR 23.337 Limit maneuvering load factors.

(a) The positive limit maneuvering load factor n may not be less than—
(1) 2.1 + (24,000 ÷ (W + 10,000)) for normal and commuter category
  airplanes, where W = design maximum takeoff weight, except that n need
  not be more than 3.8;
(2) 4.4 for utility category airplanes; or
(3) 6.0 for acrobatic category airplanes.
(b) The negative limit maneuvering load factor may not be less than—
(1) 0.4 times the positive load factor for the normal utility and
  commuter categories; or
(2) 0.5 times the positive load factor for the acrobatic category.
(c) Maneuvering load factors lower than those specified in this
  section may be used if the airplane has design features that make it
  impossible to exceed these values in flight.

Based on that regulation, the light single-engine aircraft I've flown have a +3.8/-1.52 load factor limit in normal category loading.  The aircraft is designed to structurally handle those load factors up to max gross weight.
A pilot could exceed those limits by making abrupt control inputs or "pulling G's" because by pitching up abruptly, for example, the pilot is increasing the angle of attack and accelerating the aircraft.
At speeds above Va, the wings are capable of producing enough force to damage the structure with positive or negative loading.
This is a V-G diagram (Source)

The curved line represents the load factor at which the aircraft will stall at a given indicated airspeed.
Va is the speed at which the aircraft would reach its maximum positive load factor limit at the same time it would experience an aerodynamic stall.
An angle of attack less than or greater than the critical angle of attack will cause the wing to generate less lift than it would at the critical angle of attack.  Therefore, the stall point is used to determine where the maximum load factor would occur for a given speed.
Maneuvering speed, as you can see by the chart, has no safety buffer above it, which is why Dave's answer has some details about inadvertently increasing speed.
Flying below maneuvering speed would be a better guideline to follow if you feel that there is are hazardous levels of turbulence.
Let's say you are flying well below Va, and you are hit by a strong vertical gust.  The vertical, upward, gust will increase the angle of attack by momentarily changing the relative wind, and therefore increase lift.  If that change in angle of attack exceeds the critical angle of attack, then the aircraft will aerodynamically stall rather than continue to produce greater lift. In that case, the stalled condition would protect the structure of the aircraft by acting as a limit on structure loading.
Now to answer your specific question:
It is unlikely that severe turbulence will come as a surprise during flight in a small single-engine aircraft.  I have never personally experienced turbulence where I felt the need to decrease my speed.
It is a judgement call that needs to be made by the PIC, and I would slow down whenever I am experiencing consistent turbulence that is causing me to physically perceive unusually high G-forces.
If a pilot is in that scenario, there has likely been a poor go/no go decision regarding the flight.  If you need a quantifier, "severe turbulence" would be the classification for which this matters.
I have experienced moderate to severe turbulence in flight, but those were attitude altering gusts; the load factors imposed were not near limits.

Thanks for the note. I have experienced turbulence where I felt the need to. I was flying in smooth air one night across a front and went IMMEDIATELY into a region of moderate to severe. Talk about a ride! I slowed down REALLY quick.

Indeed you can cross boundaries with abrupt changes in conditions, but my statement about it not coming as a surprise encapsulates proper pre-flight checks so that any fronts are known to the pilot beforehand, thus making it unlikely, but definitely not impossible, that severe turbulence will come as a surprise.

I agree with the preflight checks part... No turbulence was predicted that night... (No airmets)

If the load factor from the next vertical gust is likely to exceed the maximum load factor of your aircraft it is time to slow down. Now you might wonder how to know the strength of the next gust. If flying in gusty air is really uncomfortable, better slow down. It's not that you are about to break the aircraft, but being kicked about in the cockpit will severely restrict your flying skills. Flying more slowly is safer because you stay in control. Lower speed will increase the angle of attack change from the gust, but the lower dynamic pressure will reduce overall loads. Also, the lower speed translates into a less steep gust load onset ramp, which also makes flying at lower speed more comfortable.
Regarding the duration: Slow down immediately if only one gust feels like it exceeds your maximum load factor. Yes, there is a structural safety limit of 50%, and it will take thousands of gusts at the rated limit load to exceed the fatigue limit, but with gusts I recommend to play it safe. Note that the increase in safety comes mainly from avoiding piloting errors.
My worst experience was in a Katana over the Arkansas River valley. Coming from Oklahoma, the cloud cover under me increased and I was forced to continue below the clouds, flying VFR only. Below the clouds I was literally thrown around by the worst gusts I have ever experienced. To make the experience tolerable I flew more slowly than usual, but not much - I wanted not to stay too long in this kind of weather.
Gerhard Waibel once told me he was invited to fly with Karl Striedieck along the Appalachians. Now you need to know that both flew an ASW-20, a glider which Gerhard had designed. And he knows that he built in reserves! Karl's style of flying was repeatedly overloading the airframe beyond the design limit, but he never slowed down. Gerhard, certainly no wussy, said that he was seriously concerned that Karl would break the airplane, but he never did. He will turn 80 next year.

As with anything you should refer to your POH for the specific aircraft as it often covers what you should do in this very case.
For example the POH for the Piper Saratoga states

4.39 Turbulent Air Operation
In keeping with good operating practice used in all aircraft it is recommended that wen turbulent air is encountered or expected, the airspeed is reduced to maneuvering speed to reduce the structural loads caused by gusts and to allow for inadvertent speed build-ups which may occur as a result of turbulence or of distractions caused by the conditions.

Of course this is not terribly specific as to what turbulence is but its safe to say that if you feel you are going to be thrown around to the point you will begin to see speed build ups as a result of the conditions you should reduce your speed to Va.
Similarly the POH for the 172 states (P. 4-3)

Turbulent Air Penetration Speed:
2300 Lbs ......... 97 KIAS
1950 Lbs ......... 89 KIAS
1600 Lbs ......... 80 KIAS

Cessna seems to base it on load while Piper just advises a slow down to Va which is interesting.
You should also not be in the yellow arc (what ever it may be) in rough air, that is the "smooth air operating range" or "caution range". Basically the advised "slow down" is to give you a buffer area so you can inadvertently speed up and not enter the caution area or come close to Vne.
As for how much, I would say you should slow down in consistent turbulence. A single bump may just be you catching a thermal or crossing a mountain ridge etc. Turbulent air tends to persist the bumps as you move through it in which case I would slow down.
Speaking from personal experience I generally reduce speed when the ride gets "choppy" (its hard to say objectively what that is). This is somewhat a personal preference as well as for safety. The interesting thing to note is that when doing approaches in gusty conditions you may want to add speed to your approach speed.

I just want to add that the point of the speed buildup comment is not that they expect that turbulence is going to cause the plane to speed up.  What they are saying is to provide a buffer zone below Va in-case the pilot accidentally increases speed.

Va varies with weight, so both the Piper and Cessna POHs list multiple values for Va. The "turbulent air penetration speeds" you mentioned are listed elsewhere in the Cessna POH as Va.

@Dave This is where I'm at... I just need to learn from experience what the boundary is from feeling it. Too bad they can't boil that down into words.

authors: Жанибек Орынтаев


text:
Which aircraft/powerplant manufacturers use metric hardware?
The vast majority of airframes and powerplants use U.S. standard/SAE hardware. Which manufacturers of engines and airframes use metric hardware?

I believe there was a hardware spec used in Europe called ASN that was metric and was used in some European GA airplanes.

Related: Are an aircraft's nuts and bolts generally either all Imperial or all Metric, or can they be mixed?

@fooot thanks fooot. I’m aware of this post and have read the whole thing. While some good points are made, it doesn’t really answer my question... only a few examples are given.

You mean imperial measurements vs metric? RR use both, depends on the engine.

@Notts90 some use US standard, some use imperial, but I am specifically interested in who uses metric.

@Pugz none of the big western manufacturers are exclusively metric but RR does use metric for all new engines. The most likely to be exclusive are Russian manufacturers.

@Notts90 thank you. Even if it’s not exclusively metric, but some metric, I still want to know about it.

All use metric dimensions, only the numbers look sometimes rather odd.
This statement is more serious than it might look, in some places you order parts in metric dimensions and they come as 3.175 mm or 12.7 mm.
All Russian (and, by extension, all former East Bloc country) engines use metric dimensions. You only see fewer of them.
I am less sure about French engines like the CFM-56 which uses a GE-designed hot section, but the fully French-designed engines use metric, too.
In the GA world the modern Diesel engines are all metric.

Can you please elaborate on what you mean by “all use metric dimensions”? I’ve been working on several power plants and airframes - Cessna, Piper, Grumman, Beechcraft (King Airs), P&W PT-6 turbines, Lycoming, Continental, and all seem to use SAE only dimensions and fasteners/hardware.

@Pugz: OK, you didn't get it. Use a metric caliper. Measure some dimensions. You will get metric dimensions, right? Even from a US engine.

Lol that’s funny. I kind of thought you were saying that but didn’t take it seriously. Nice joke.

After all, 1 inch is, by definition, exactly 25.4 mm...

@xxavier: Yes, you are right: The imperial units are defined by the corresponding SI units. Therefore, the inch is now defined as 25.4 mm. Want more precision? OK: 1 inch = 25.400000000000000000 mm. Therefore, all dimensions are metric but with odd numbers. This joke has more depth than appears on first reading.

@PeterKämpf Well, yeah :)) - Then again it's rather shallow, not really working so simple, as metric bolts are made to ISO pitch/lead while 'imperial' bolts are defined by the ANSI maintained "Unified Inch Screw Threads Standard".So while a 3/8 bolt does measure about 9.5 mm, a 9.5 mm nut won't run along. Diameter is just one of 6 major (and mord than a dotzend secondary) values to describe such a simple piece :)) And yes, it's relevant, as the OP asked for SAE specifications. Standards include way more than just the way length is counted.

@Raffzahn: You need to stay consistent, of course. Taking diameter from ISO and thread pitch from SAE won't work. And there is no such thing as a 9.5 mm nut, at least not in the standard ISO sizes.

@PeterKämpf Well, almost, as there are not standard sizes given, just recomended much like in the prior DIN standards  That's as well a difference between ISO and SAE, as the later only defined discrete sizes. Also, not really woth to argue about an example size when it's about the underlaying mechanics, isn't it?

This is all great trivia, but I was already aware of this and it’s not particularly helpful pursuant to my original question. The fact that the inch is in actuality defined by a metric value is not helpful in answering my question. Any actual answers? Tools are not specified in such a way, and I’m pretty sure you know what I’m actually asking :-)

@Pugz: So you think that Russian or Chinese or French engines also use imperial units? If you can't handle a honest answer, why do you ask in the first place?

@PeterKämpf Airbus uses mostly SAE hardware on their airframes. Of course the commies use metric. I would prefer everyone use metric. But they don't. In the non-communist world (most of the world) most companies use SAE or Whitworth on aircraft, because of the historic aircraft tooling being in inches after the fall of Hitler's Europe and the growth of the aviation industry in the west that outpaced the growth in the east. This answer falls short of helping me know who uses metric hardware (bolts,screws, nuts, etc.). I would appreciate some guidance of which manufacturers use this. Thanks!

@Pugz: In my flying club we use both - the Rotax and Limbach engines of the motor gliders have metric parts while the Lycoming on the tow plane has tools in imperial units. I tried to give you a rule to determine who uses what; an explicit list would be rather long.


text:
Legal to land on a beach?
If you have a plane like a Cub or Scout, is it legal to land on a beach, river bank, or other similar feature or will the FAA take your certificate if you do it? I can't find any info on this anywhere but see lots of YouTube videos of people doing it.
This question is not in reference to an airplane with an emergency, I'm talking about a voluntary, intentional landing on a beach with the purpose of fishing or camping, like is done with many bush planes.

You'll probably get in trouble if you're stupid about it.

They should have some kind of horn on an airplane to get everyone everyone off the beach before it lands

@Ethan - The only reliable such horn on an aircraft in a condition such that it needs to set down in a hurry would be a compressed air horn, which is just one more piece of equipment that would have to be checked during the annual but rarely used. Other issues such as the need to shield the horn from wind blast (otherwise the back pressure would silence it) are fairly easily dealt with but can reduce the directionality and volume of the horn, and thus the ability to alert the very people you have it for in the first place.

Haha, that's good stuff.

Copalis State Airport is literally a beach

@ob318 There is no reason to put "under FAA regulations" into the title, as the question is already tagged such. Per this StackExchange Meta question it is simply not needed, even for search engine optimization.


text:
Does the first portion of a trip that was < 50nm count as XC on a long trip?
I flew a long trip (> 900nm) but the first leg, where I had a full stop landing to pick someone up, was only 24nm away from my starting point. For the FAA, a cross country trip counts as > 50nm straight line distance from the starting point. How should I log this short leg of the greater XC trip? Just count it all as XC or just subtract the time of the short leg from the XC total in my log book?

@mins lol nice.

The relevant regulation is in 14 CFR 61.1(b)(3):

Cross-country time means—
(i) Except as provided in paragraphs (ii) through (vi) of this
  definition, time acquired during flight—
(A) Conducted by a person who holds a pilot certificate;
(B) Conducted in an aircraft;
(C) That includes a landing at a point other than the point of
  departure; and
(D) That involves the use of dead reckoning, pilotage, electronic
  navigation aids, radio aids, or other navigation systems to navigate
  to the landing point.
(ii) For the purpose of meeting the aeronautical experience
  requirements (except for a rotorcraft category rating), for a private
  pilot certificate (except for a powered parachute category rating), a
  commercial pilot certificate, or an instrument rating, or for the
  purpose of exercising recreational pilot privileges (except in a
  rotorcraft) under §61.101 (c), time acquired during a flight—
(A) Conducted in an appropriate aircraft;
(B) That includes a point of landing that was at least a straight-line
  distance of more than 50 nautical miles from the original point of
  departure; and
(C) That involves the use of dead reckoning, pilotage, electronic
  navigation aids, radio aids, or other navigation systems to navigate
  to the landing point.

Note that the rule under paragraph (ii)(B) is "a flight" that includes "a" point of landing more than 50nm from the point of departure.  It does not specify that all points of landing must be further than 50nm from the departure point, or even that the first point of landing must be further than 50nm.
Since the overall trip was over 50nm, does the FAA allow you to consider that 24nm leg to be part a single overall flight?  Unfortunately, the FAA doesn't provide a definition of "flight" in this context.  However, it is generally accepted that short stops (to pick up a passenger, refuel, eat lunch, etc.) can be logged as part of a single flight.
Edit to add:  Please also this this previous question, and especially the AOPA article it links to.


text:
When airplanes first got windows, what material was used?
When airplanes were first introduced they were open cockpit - but soon enclosed cockpits were developed. What were the first materials in use for airplane windows? I don't believe plexiglass existed back then.

The first aircraft to have any sort of protection for the pilots had windshields made of glass, which offered some protection against propwash and wind. These were flat glass panes, which were later replaced with laminated glass.
The first aircraft to have anything similar to the modern canopies were the Royal Aircraft Factory SE4 and SE5, which had canopies made up of celluloid- and which was promptly remove by crews once these reached squadron service (during WWI).

Royal aircraft factory SE5, image from forums.ubi.com
Later, tempered glass was used after the WWI. As the aircraft altitude and speed increased, closed canopies became the norm and before WWII, acrylic canopies came to be used.


text:
Can a GA magneto-spark plug ignition survive an EMP?
Can the coil and capacitor (condenser) magneto/spark plug ignition system as exists on most general aviation aircraft survive an EMP? Let's talk about a standard Lycoming or Continental engine. How about most turbine engines? I'll use a PT-6 as an example. I assume the FADEC would be toast? How about other parts of the electrical system such as the battery? Is there any data or research on this?

Can the coil and capacitor (condenser) magneto/spark plug ignition
  system as exists on most general aviation aircraft survive an EMP?

Like anything it depends on the EMP's strength, the angle of incident to the device and the device in question. The various things in an aircraft will break down for different reasons. But for the rest of this lets assume an EMP that is sufficient to fry stuff. A magneto will suffer toasted coils as the induced current could potentially generate enough heat to degrade the resin coating on the wire they use on coils. It should however be noted that the magneto is more than likely shielded to prevent interference with avionics which will play out in your favor here.

How about most turbine engines? I'll use a PT-6 as an example. I
  assume the FADEC would be toast?

Most likely yes. Again the unit is generally housed at least in some capacity in a shielded case but modern PCB components don't play nice with large induced currents. Turbines do have an Igniter system that may see some damage depending on the severity.

How about other parts of the electrical system such as the battery?

Things like interior lights will most likely blow out, batteries (depending on type and casing) could go. Overheating is a concern if enough current is forced over the line.

Is there any data or research on this?

There is some Mil-Specs (MIL-STD-1541 (USAF)) out there that cover it for the military. This question covers it for airliners. You can find at least one book on the topic here. There was a lot of research on this that pertains to missile systems as one anti-missile defense was to detonate a nuke in front of the oncoming unit. If the blast did not take it out the resulting EM field would fry what ever guidance and control systems were on board (assuming it was not ballistic). As such, work went into making the units EMP hardened. I'm not sure that work is very public though. The soviets were big users of vacuum tubes as they believed them to be far less susceptible to EMP's. It looks like this company does testing and research on EM hardened aircraft.

All electrical devices are susceptible to EMP to varying degrees. EMP causes a disruption in the electrical and magnetic field (see Wikipedia).
The magneto uses magnets and coils to generate AC pulses. When a strong magnetic or electric field passes through such a system excess current and voltage would likely be introduced and so a device who's operation depends on magnetic fields would likely falter (though maybe not fail) during a magnetic event.
One concern is that all discrete electric components have sub-components (usually insulation) that have a maximum breakdown voltage. The wires in a coil have a thin insulation on them to keep from shorting to other coils or the component body. A high voltage spike could cause that material to fail and create a short.
Another concern is that large currents amplified via transformers could cause other components (and even the transformers themselves) to fail like during the 1989 geomagnetic storm. In your aircraft a few critical items could cause a similar failure. The ignition coil could amplify current flow on the battery side of the system. While a fuse would likely blow in this scenario it's conceivable that a string of smaller pulses wouldn't trip the breaker and could damage the battery or other components on that system.
If a high voltage/high current system like a power station can be effected it seems likely that a close pulse to an aircraft would cause similar failure, or at least degradation, to discrete electrical components.

Transformers are vulnerable to geomagnetic storms because power lines make excellent antennas and pick up a lot of power. In the absence of large antennas, it's unlikely that simple components, like coils, will be damaged by EMP.

Concerning ignition, and if no semiconductors are used (some capacitor-discharge systems use SCRs) there is little possibility of any damage, since coils, capacitors or mechanical switches can withstand very high transient currents.

Do you have any supporting data that explains this? I had exactly the same feeling but no data.

Coils are generally inside a metal box which will act as a faraday cage, so the coil itself won't be affected. Most wires in aircraft are (relatively) straight, short and thin reducing the induced current.
Assuming 'sufficiently strong' EMP, the most likely components to suffer damage are shunt or smoothing capacitors which are non critical


text:
What is the ICAO equivalent of /G in a flight plan?
How should I fill out an ICAO flight plan if I have a Garmin GNS-430W WAAS certified unit? I file as /G in the US domestic format.

Welcome to the site! I edited your question to make it - hopefully! - a little clearer but if I've got anything wrong you can always edit it yourself to correct it.

I have a GNS-530W, which is identical to your unit except with a bigger screen and I file ICAO with a G, B, and S, which are GNSS/GPS, LPV, AND VOR/ILS, respectively, to indicate the equipment I have on board. Technically just the G would be sufficient but I list all I am capable of to assist ATC in routing me most effectively or in the event of an emergency.
This would be entered on the form as "G, B, S"
Here is an excellent article explaining the new fields and codes for filing ICAO as the FAA domestic flight plan form comes to an end soon:
Filing ICAO Flight Plans in ForeFlight